Investigations of antigen-antibody systems frequently require sensitive methods for the detection of each component. The course of an infectious disease, for example, can be followed by determinations of the presence or absence of antigens or antibodies in serum, and their relative amounts. At the outset of the disease, the antigen will be in excess. As the body marshals its defenses, the relative amount of antibody present increases. When the infection subsides, the ratio of antibody to antigen increases until, finally, there is no detectable antigen.
Sensitive detection of antigenic substances is conveniently carried out by a solid phase competitive radio-immunoassay (RIA). This procedure cannot be used, however, if the test sample contains antibody since this will interfere with the radioimmunoassay.
A solid-phase procedure which makes possible the accurate determination of either antigen or antibody particles in the presence of the other would be a significant advance in the art.